Preparation of p-nitrodiphenylamine



liant- March 8, 1960 HEAO VERT/WL 754/175' UFF P. L. MERZ Filed Deo. '7, 1955 IN VEN TOR.

GE/FIS TYPE APP/117x470@ .AITORNEY 232159431 f Y rREPARATIoN 1? p1-IITRODIPIillill*IYLAlYiIlIEy ice f 2L ravity is signiicantl'yy different froirrthat-i` ofv water. The

specific gravity of-'anilineI 20V i Y (1.0275) is too;'close to that of1water top ermit. a clean separation Paul,y L. Merz, Naugatuck, Conn., lassignorv to United y States Rubber Company, New York,4 NX., acorporation of New York Y Application December 7',1955,'SerialNo;'551,579'

1 claim. (ci. 26o-5761) This invention relates to an improvement; in the facture of'p-nitrodiphenylamine.

Previously, a well-known method-of synthesizing the i of excess of' aniline or nrtrobenzene A disadvantage; loi. the-Goldberg gsynthesis is that thev amount of p-nitrodiphenylamine produced iS SQ small (fca'. 1% of' theory)U as to make` thei'p'rocess non-cornmercialf. The reasomforthis has new-A been foundito1be-v the presence duringthe react-ion l' off the relativelysmall 'amount of-fwatereformedbyA the neutralization--offjthe hydrochloric acid-whichgsurprisingly/fis notisufliciently removed duringthegreilnxingfoperatiqn by Goldberg, in spite o f the high' temperature of reiluxj.V The` Vr rnole Qffwormedrwater; about' 9" grams- 'in-.a total reaction mixto have an inhibiting effect on the formation of p-nitrodiphenylamine, with consequent reduction in its yield.

I have found that if particular care and attention is given to the removal of the formed water from the zone of reaction, that the yield of the desired chemical is iny a` Starleand Dean type. trap. In orderv to use a Stark and Dean type.t1`ap;.asmal1 .amount of a suitable inert, -azeotroping solvent which possesses@ a boiling point lsi'gnilicantly lower. than. aniline, is charged into eitherthe reaction mixturefor the empty- Starkand Dean trap prior 'ture of more than ltlilgrams, has"nowbeen'disoovered 'action vessel. Thus.l allv wateris to .thefreaction zone.,

to starting the reaction.. This Starkand Dean type separator is shown in the .attached4 drawing and isillustrat'ed in.Examp1e:3, wherefbenzene was employedas the azeotroping solvent. The; water. azeotrope distilling up into thevertical condenser, attachedA to the Stark and Dean trap, condenses` andruns backintoj the trap.. where; the water separates out. It is, apparent that both the process employingA a. f ractionating column. and thatemployingI a Starloand' Dean type; trapare. capable ofv continuously `removingl water from the reaction and are distinctrfrorn the; Goldberg-proces s which operatesunder totaLrelluX bymerely, having a, rcllux condenser, attached tofthe recontinuously,r returned The following examples illustrate the ention` in more detail, parts beingjbyweightfff Onevv mole proportion of p-nitrochlorobenzerie,V 9I`rnoles of aniline,` 0.7 mole of powdered potassium carbonate 'and 0.0075 mole of. cuprous iodide, were chargedinto a twoaliter, 3 -necked flask equipped with thermometer, motor-driven, stirrer, addition funnel, and vertical.v aircooled fractionatingl, column. The top of this air condenser was fitted with a simple ldistillation headleading to a water-cooled take-off condenser. The reaction mix' ture was heated to between 184 C. and 188 C. for 21 hours. Boiling at this temperature was sutliciently heavy to drive off the lower boiling fractions (B.P. 150 C.-

' 180 C.) which consisted of aniline-water azeotrope,

increased about 70 fold. This result could not have been foreseen because in many reactionsof this type the presenceof a small amount of water is actually helpful.

According to the present invention, the said water' is` removed continuously as fast as it is formed throughout the course of the reaction, thereby allowing the reaction,

once started, to be conducted under substantially an- Y hydrous conditions. This removal is practically achieved by oontinuouslyrdistilling oit the water throughout the course of the reaction.

accompanied by a very large amount of the co-distilling aniline solvent, it is advantageous to utilize a fractionating column or a trap of the well known Stark and Dean type for the purpose of separating the water from the reiluxing solvent.

vThese two methods of removing water. are compared with the Goldberg type apparatus in the accompanying drawings. In the iirst, a fractionating column equipped with a distillation head and a take-off condenser is attached to the reaction flask. Advantage is taken of the fact that aniline and water forman azeotrope which is easily distilled ol the top of the fractionating column while anhydrous anilineret-urns to the pot.

Removal of water by a Stark and Dean type trap requires the use of an azeotroping solvent whose specic Since a simple distillation of this small amount of water from the reactionwould be which as stated, above is freed of water and the Waterfr'eeaniline returned to the reaction mixture.

`At the end of 2l-hours the reaction mixture was Vcooled and then iiltered to remove the inorganic salts.

The filtrate was distilled to recover any excessl of unreacted aniline and the distillation residue then steamv blown to remove the unreacted p-nitrochlorobenzene and any residual aniline. The recovered p-nitrochlorobenzene amounted tol 38 g., i.e., 24% of the original charge. The residue consisted of hard green crystalline lumps which upon recrystallization from hot methanol yield 156 g.

the small amount of water. vious reason why the relatively insignificant amount of (73% of theory) of moderately purel(My.P. 122 C.- 129 C.) p-nitnodiphenylamine. I

The Example 2 below represents Goldbergs procedure in which his mixture is simply heated under reux in a reflux apparatus, no provision being made to accommodate the removal of water, because there was no recognition of the importance of the presence or absence of A priori, there is no obwater must be removed, since the reaction is irreversible because of the liberation of the carbon dioxide; nor that the small amount of water would be sutlicient to inhibit the condensation.

j retreated Mar. s, 196eV vis too slow to beY practical.

Example 2 A mixture identical with the above (1.6., 1 mole of pnitrochlorobenzene, 9 moles of aniline, 0.7 mole of po- .tassium carbonatevr and L0.0075 mole cuprous iodide) -was heated in a reiiux apparatus atA 189` C., asv described by Goldberg, for 22 hours under total reux. The reaction mixture was worked up -in exactly the same way as the preceding example. distilling olvthe excessaniline, and steam distilling oi the unchanged p-nitrochlorobenzene, only an insignificant quantity of solid residue remained. Upon recrystallizing the residue from hot CH3OH a small amount (ca. 1% of theory) of moderately pure (M.P. 125 C.- 134 C.) p-nitrodiphenylamine was obtained.

The conditions and the proportions of ingredients cited in the foregoing reaction can be varied vover a considerable range without unduly aiecting the reaction. Thus the mole ratio of aniline/p-nitrochlorobenzene may be varied from 1 to 10, per mole of the latter, and the mole ratio of potassium carbonate/p-nitrochlorobenzene may vary from 1/2 to l, per mole of the latter. An even larger excess of potassium carbonate is not detrimental. Any suitable copper salt, such as cuprous iodide, cuprous chloride or copper sulfate, may be used. The reaction temperature can be varied from 170 C. to 200 C. At temperatures below 170 C. the reaction rate At reaction temperatures above 200 C. impure reaction products which' are difcult to purify are obtained. Preferred temperatures are in the range from about 180 C. to about 190 C.

a 500 cc., 3necked ask equipped with thermometer, i f

motor-driven horseshoe stirrer, Stark and Dean trap and redux condenser. The reaction mixture was heated on a Woods metal bath and sufficient benzene was added to give a reflux temperature of 185 C. The theoretical amount of water was evolved in 26 hours time. The reaction mixture was then cooled and the crude p-nitro v381,230

After ltering ott the inorganics,

l diphenylamine isolated by the procedure described in 'Examples 1 and 2. 157.5 g. (74% of theory) of p-nitrodiphenylamine, M.P. 115 C.-125 C. were obtained. This product was purified'by vacuum distillation; B.P. 181 C.-200 C./0.3 mm. The yield of pure p-nitrodiphenylamine, M.P. 130 C.-133 C., amounted to 134 g. or an 85% recovery from the crude material.

As mentioned above, maintenance ofanhydrous conditions through removing the water formed by the" revaction of HC1 with K2CO3, is absolutely necessary. In general, however, the removal of water should not be carried much beyond the theoretical point, and thus-the reaction is usually stopped when approximately l mole of water per mole of p-nitrochlorobenzene have been evolved.

Having. thus described my invention, what I claim and desire to protect by Letters Patent is:

In a process for the preparation of p-nitrodiphenylamine by subjecting a reaction mixture in which the active ingredients consist essentially of from l to 10 moles of aniline, 1 mole of p-nitrochlorobenzene, and y to .l

mole of potassium carbonate asa hydrochloric acid acceptor. together with a catalytic amount of copper salt to reaction at a temperature in the range of 170 C. to 200 C., thewimprovement which comprises conducting said reaction under substantial anhydrous conditions by removing all water, including the water formed by the neutralization of the hydrochloric acid with said potassium carbonate, from the reaction zone throughout the course of the reaction by continuously distilling ott said water as an vazcotrope with an azeotroping agent selected from the group consisting of aniline and benzene.

` References Cited in the le of this patent Y I UNrTapfs'rA'rEs PATENTS Fret. Jan. 12, 1932 2,028,074 Lauter f f.. Ian. 14, 1936 2,476,170 Widiger July 12, 1949 2,656,389 Johannesen Oct. 20, 19,53

2,700,060 Cherlow et al. Ian. 18, 1955 FOREIGN PATENTS 185,663 Germanyv Apr. 22, 1906 France Nov. 3, 1906 

